Alloy steel



United States Patent ALLOY STEEL Peter Payson, Pittsburgh, Pa., assignorto Crucible Steel Company of America, Pittsburgh, Pa., a corporation ofNew Jersey No Drawing. Application February 24, 1958 Serial No. 716,856

3 Claims. (Cl. 75-126) This invention relates to a low alloy steelsuitable for the manufacture of hardened bars and, more particularly, toa low cost alloy steel which can be air cooled from an austenitizingtemperature to form martensite.

Although not limited thereto the present invention is particularlyadapted for use in the manufacture of homogeneous jail bars. As the nameimplies, homogeneous jail bars are those composed of a solid metal masshaving the same composition throughout. resist shattering by a blow orbending stress and must resist cutting with a hacksaw. Furthermore, thebars should be simple toheat treat and should be kept straight duringthe heat treating operation.

According to the prior art, homogenous jail bars were manufactured froma simple carbon AISI 1060 steel of approximately 0.55% carbon and 0.70%manganese. In order to harden a steel of this type to resist cutting, itmust be water quenched from the range of 1500 to 1550 F. The quenchingprocess produces hard martensite on the outside of the bar to resistcutting and relatively ductile pearlite on the inside which gives highresistance to bending stresses. As a consequence of the Such bars must.

water quench, however, the bars may warp or twist. At- I tempts havebeen made to maintain the bars straight during the quenching operationby securing them in a rigid fixture. This procedure, however, isunsatisfactory since the bars may fracture due to their inability toexpand in the fixture. Anothermethod heretofore used was to quench thebars to a temperature of about 500 F., at which point they werestraightened in a press. The difficulty with this latter method is thatif the bars have hardened before straightening they will fracture in thepress as they do in the fixture. Thus, no satisfactory means hasheretofore been employed to maintain the bars straight during thequenching process.

As will become apparent from the following detailed description, I havefound that an alloy can be prepared which may be air hardened wherebythe difiiculty of maintaining the straightness of elongated members inthe hardening operation is minimized. Specifically, my alloy consists ofa medium carbon steel having relatively small amounts of manganese,silicon, chromium, and molybdenum added thereto. By proper control andadjustment of this composition and by air hardening from theaustenitizing temperature range of 1600" F. to 1750 F., I can providesteel bars relatively free from residual stresses having a hard outersurface in the range of Rockwell C 63 to 65. Microanalysis will revealthat with this alloy the bar is martensitic after air cooling. Inaddition to minimizing straightening difficulties during cooling, thealloy also has high resistance to softening during tempering and hasgreatly improved toughness characteristics over water quench bars formedfrom A181 1060 steel; however, the amounts and types of alloyingconstituents added to my composition are such that the overall cost ofthe final product is not materially increased over the AISI 1060 bars.

, 2,914,401 Patented Nov. 24, 1959 In accordance with my invention, Iprovide bar steel of the following broad" and preferred compositions:

ANALYSIS, PERCENT BY WEIGHT Broad Preferred C 55/. 60/. 70 Mn 70/1. 50.90/1. 20 Si 1. 2012.00 1. 40/1. Cr. 1.00/2. 50 1. 30/1. M0 50/1. 2060/1. 00

Steels in the foregoing range of composition have a minimum Rockwell Chardness of 63 when air hard-- ened from a temperature of 1700 F. Theycan be tempered by holding at temperatures from about 200 F. to 300 F.for one hour or longer followed by an air cool while retaining a minimumRockwell C. hardness of 63. Furthermore, they have good hot workabilityand should not present difficulties in rolling.

Properties of my new and improved steel are established by thefollowing: Eight 30 pound induction heats, having the analyses given inTable I, were heated to 1975 F. and forged into 1% inch bars, the barsbeing subsequently stress relieved at 1350 F.

Table I Grade 0 Mn P S Si Ni Or M0 0. 57 1. 00 0. 005 0. 027 l. 17 0.09 1. 73 0. 76 0. 58 0. 88 0. 005 0. 026 1. 25 0. 09 2. O2 0. 76 0. 65l. 03 0. 005 0. 027 1. 82 0. 09 1. 64 0. 76 0. 62 1. 78 0. 006 0. 027 1.94 0. 09 1. 61 0. 76 0 70 1.02 0. 007 0.028 1. 23 0. 09 1. 64 0. 76 0.72 1. 68 0. 007 0. 027 1. 20 0. 09 1. 49 0. 76 O. 72 1. 13 0. 0060.026 1. 77 0. 09 1. 74 0. 76 0. 72 l. 76 0. 006 0. 027 1. 77 0. 09 1.91 0. 76

Ater the bars were stress relieved, five specimens (each /5 inch thickby 1% inch and 1% inch) were cut from each bar and heated toaustenitizing temperatures ranging between 1450 F. and 1750 F. for onehour as shown in Table II. Thereafter, each specimen was air cooled toroom temperature in still air.

Table H Rockwell G"'Hardness After Air Cooling from a -AustenitizingTreatments 1 Grade 1,450 F. 1,650 F. 1,650 F. 1,700 F. 1,750 F. I

1 Austenitlzing treatment consisted of heating a specimen for one hourat each of the indicated temperatures.

It can be seen from Table II that as the austenitizing temperatureincreases from 1450 F. to 1700 F., the Rockwell C increasesprogressively. Above 1700 F., however, the Rockwell C hardness drops offafter .the specimen is air cooled. The microstructures of various steelsin Table II show that they consist essentially of martensite after beingaustenitized from about 1600 F. or higher and air cooled. It is apparentthat with the composition of the present invention, substantially nohigh temperature transformation from austenite to pearlite occurs whenthe alloy is heated above the 1600 F. point.

Table III shows the results of tempering specimens C,

E and F after being air hardened from 1650" F.

3 Table III Rockwell "C Hardness After Tempering 1 Belore tempering, thespecimens were austenitized at 1,650 F. for one hour and air cooled.They were then tempered cumulatively for one hour at each of theindicated temperatures and aucooled.

It can be seen from this table that the Rockwell C hardness issubstantially unimpaired when the metal is heated to 200 F. for one hourand allowed to air cool. As the tempering temperature progressivelyincreases from 200 F. to 300 F., the Rockwell C hardness decreases butnot to any appreciable extent.

The results of deflection tests on three of the steels of Table I arecompared with AISI 1060 steel, a composite jail bar and a homogeneousinduction hardened steel bar in Table IV. Two specimens, 14 inches inlength, of each of the grades C, E and F were machined to 1% inchdiameters and heated to 1625 F. and 1675 F., respectively, and cooled inair.

1 The specimen (14 inches long and 1% inches in diameter) was cooled instill air after being austenitized at given temperature.

1 Hardness readings were taken on the broken test piece after grindingtwo surfaces mutually parallel to the longitudinal axis of the specimen.

Specimen was 14 inches long and 154 inches in diameter.

The regular composite bar of Table IV consists of an austenitic steelmatrix provided with high carbon tool steel inserts. With thisparticular construction, the austenitic steel matrix gives resistance toshattering by blow or bending stresses while the high carbon tool steelinserts prevent cutting with a hacksaw. The homogeneousinduction-hardened bar consists of AISI 1060 steel having only its outersurface heated to an austenitizing temperature in an induction coilbefore quenching. The entirety of the AISI 1060 bar was, of course,heated to an austenitizing temperature and then quenched. It can be seenthat the steels of the present invention have a much higher resistanceto bending stresses than the steels used in the prior art. Specifically,the resistance to bending stresses in specimen C is almost four timeshigher than that of a regular composite steel bar and about twice ashigh as the regular AISI 1060 steel and the homogeneous inductionhardened steel.

It can thus be seen that I have provided an air hardenable jail barhaving a high hardness and high resistance to bending stresses afterbeing air cooled from an austenitizing temperature. Although I havespecifically described the invention in connection with jail bars, itshould readily be understood that the steel is equally applicable forother wear resistant articles such as dies, gages, shear blades, cutterbars for lawn mowers and the like, chuck jaws, cams, boring tools,clinker bars, and generally such tools as have considerable length inproportion to diameter and are, therefore, difiicult to maintainstraight when they are hardened by a water or oil quench.

I claim as my invention:

1. An alloy steel consisting essentially of about .60 to .70% carbon,.90 to 1.20% manganese, 1.40 to 1.80% silicon, 1.30 to 1.90% chromium,.60 to 1.00% molybdenum and the remainder iron with the usualimpurities, characterized in being hardened to a minimum of Rockwell C63 by air cooling from an austenitizing temperature.

2. An elongated steel article of manufacture having a length many timesgreater than its longest cross sectional dimension and comprising about:.60 to .70% carbon, .90 to 1.20% manganese, 1.40 to 1.80% silicon, 1.30to 1.90% chromium, .60 to 1.00% molybdenum, and the rest iron with theusual impurities, characterized in being hardened to a minimum of aboutRockwell C" 63 by air cooling from an austenitizing temperature.

3. A jail bar consisting essentially of about .60 to .70% carbon, about.90 to 1.20% manganese, about 1.40 to 1.80% silicon, about 1.30 to 1.90%chromium, about .60 to 1.00% molybdenum, and the remainder iron with theusual impurities, characterized in being hardened in sections up toabout 1 /2 inches in diameter to a minimum of about Rockwell C 63 bymaintaining the same within the approximate temperature range of 1600 to1700 F. for about one hour and thereafter air cooling.

References Cited in the file of this patent FOREIGN PATENTS 517,118Great Britain Jan. 22, 1940

1.
 3. A JAIL BAR CONSISTING ESSENTIALLY OF ABOUT .60 TO .70% CARBON,ABOAUT .90 TO 1.20% MANGANESE, ABOUT 1.40 TO 1.80% SILICON ABOUT 1.30 TO1.90% CHROMIUM, ABOUT .60 TO 100% MOLYBDENUM,A ND THE REMAINDER IRONWITH THE USUAL IMPRURITIES, CHARACTERIZED IN BEING HARDENED IN SECTIONSUP TO ABOUT 11/2 INCHES IN DIAMETER TO A MINIMUM OF ABOUT ROCKWELL "C"63 BY MAINTAINING THE SAME WITHIN THE APPROXIMATE TEMPERATURE RANGE OF1600 TO 1700*F. FOR ABOUT ONE HOUR AND THEREAFTER AIR COOLING.